Table 1.

Definition and usage of terms in human and veterinary vaccine evaluation.

term		definition
vaccine potency	veterinary	‘relative strength of a biological product as determined by appropriate test methods. (Initially the potency is measured using an efficacy test in animals… with pathogen challenge;… later this may be correlated with tests of antigen content, or antibody response, for routine batch potency tests.)’ [5]
	human	‘potency is the specific ability or capacity of the vaccine as measured by a laboratory test’ [6]
	difference	similar definition but less frequently used for human vaccine evaluation
vaccine efficacy	veterinary	‘specific ability of the biological product to produce the result for which it is offered when used under the conditions recommended by the manufacturer’ [5]
		‘the ability of the vaccine to give protection against the adverse effects of the infection to the vaccinated animal...’ [7]
	human	‘...the percentage reduction in disease incidence attributable to vaccination [usually] calculated by means of the following equation: 1.1 where RU = the incidence risk or rate in unvaccinated people and RV = the incidence in vaccinated people … measured in an individually randomized placebo-controlled clinical trial’ [1]. The equation for vaccine efficacy can be reformulated as: 1.2 where RV/RU is the relative risk or rate ratio.
	difference	veterinary usage has not been standardized
vaccine effectiveness	veterinary	usually not a specific term, more the ability of a vaccine to control disease in the field [8]
	human	vaccine efficacy measured by observational studies under field conditions within a vaccination programme [1] or measured by trials conducted under normal programme conditions
correlate of protection	veterinary	a variety of terms are used to describe this widely used concept
	human	a specific response to a vaccine that is associated with protection against infection, disease, or other defined endpoint [9,10]
vaccine coverage	veterinary	as for human—although occasionally it refers to the proportion of the target population that have sero-converted to a protective titre; the latter is sometimes called immunization coverage or population immunity [11]
	human	the proportion of the target population that have been vaccinated according to a defined schedule. Sometimes called immunization coverage [12]
	difference	occasionally in veterinary programmes ‘immunization coverage’ may refer to the proportion that have sero-converted above a titre deemed protective